Keep an eye on the number of live visitors in the browser tab. It displays the number of visitors in the last 30 minutes in the browser tab.
Live Plugin that shows the current number of visitors on the page.
This Piwik plugin adds a new report visualization: the treemap.
Piwik Plugin to track whether visitors are using IPv4 or IPv6
Plugin to automatically create Annotations by polling a feed (Atom/RSS)
Provides security information about your PHP environmont and offers suggestions for improvement based on PhpSecInfo from the PHP Security Consortium.
This plugin is a developer tool that will generate fake visits. It's only useful if you're creating your own Piwik plugin or theme.